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Figure 4.
Figure 4. Stereo Views of the Functional Sites in
PI-SceI(A) The protein self-splicing site containing the
essential N-terminal Cys-1 and C-terminal Asn-454 residues
viewed from the back of domain I, as shown in Figure 2. His-79
and His-453, positioned proximal to the terminal residues, are
extremely conserved between self-splicing proteins and could
perform as general acids/bases in the autocatalytic splicing
reaction. Three of the β strands that are identified are
further linked to subsequent strands in the site shown (e.g.,
β3 to β6, β7 to β8, and β24 to β28).(B) The endonuclease
active site containing the charged cluster of three residues
(see text). The orientations of the two symmetry-related α4 and
α7 dodecapeptide repeats are similar to those shown in Figure 2.
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